Detection of bodies

ABSTRACT

Detection of the presence of an animal body, for instance a human, in a detection zone is achieved by generating a low power LF field ( 17 ) between antennae ( 12, 18 ), and by measuring the disturbance of this field by the body. An analyser ( 16 ) is used detect such disturbance by measuring changes in the phase of the received signal ( 19 ).

FIELD OF THE INVENTION

This invention relates to the detection of animal bodies such as thebody of an intruder. The invention provides both a method of andapparatus for detecting the presence of an animal in a detection zone.

BACKGROUND TO THE INVENTION

Various systems are well-known for the detection of intruders, forinstance movement sensors and both passive and active infra reddetectors. It is also well-known to detect the presence of a conductive,inanimate, object by its influence on a magnetic field, for instance theposition of a movable magnet relative to a reed switch. It is an objectof the present invention to provide an improved method and apparatus fordetecting the presence of an intruder, or the like, in a detection zone.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method of detecting ananimal body, comprising generating a low frequency radio (LF) detectionfield and detecting a phase change in the field caused by the presenceof the body in the detection field.

Throughout this specification the term “low frequency” (“LF”) has theinternationally-accepted meaning of 30 kHz to 300 kHz. In practice, thefrequency will be selected to take account both of local regulatoryconditions and of the ambient conditions appropriate for detection of anintrusive object; thus the frequency or frequencies are chosen so as notto interfere with local transmission frequencies and to ensure that theintrusive object will alter the detection field. References in thespecification to “animal” include both living and dead bodies, and theinvention is not limited to the detection of mammalian species.

The method preferably includes using a transmit antenna to generate thefield and using a receive antenna to detect any change in the detectionfield.

Preferably, a method according to the invention for detecting theapproach of a body towards a protected area or protected opening to anenclosure, includes using a transmit antenna close to the protected areaor opening and a receive antenna spaced horizontally from the transmitantenna away from the protected area or opening, monitoring the phaseand amplitude of the signal received at the receive antenna, andgenerating an alarm signal only in response to a change in phaseaccompanied by an increase in amplitude.

Alternatively, for a higher level of discrimination, the method mayinclude using at least one additional receive antenna, and using theoutput from these receive antennae to detect the direction in which theobject moves through the detection field and/or the position of the bodywithin the detection field.

The method preferably includes detecting the change in the detectionfield by measuring the phase of the signal received at a receive antennain the absence of any animal in the detection field, and by monitoringthe received signal to determine when the phase of the signal haschanged by more than a predetermined amount.

The method may include generating the field at a predetermined frequencyand detecting the entry of an object into the detection field bymeasuring any change in the phase of the LF signal received by thereceive antenna.

The method preferably includes taking a reference signal from atransmission signal to the transmit antenna, and equalising thisreference signal with a received signal from the receive antenna toensure that there will be no phase shift between the transmission signaland the received signal when the detection field is free from intrusionother than that due to the distance between the antennae.

The method may include modulating the LF signal.

The method preferably includes sampling the transmitted and received LFsignals in the absence of an intrusive object in the detection zone,using these samples to determine a base condition for the phase values,and comparing the received signal with this base condition. In this casethe method preferably includes determination of the base conditions attwo or more frequencies, generating the detection field at one frequencyuntil the possible presence of a body is detected with reference to thebase condition at that frequency, and then changing the LF frequency toconfirm such intrusion with reference to the base condition at thesecond frequency.

The method preferably includes performing a frequency scan of thefrequency spectrum to be used to determine the background noiseenvironment, selecting the frequencies which exhibit least noisecharacteristics, storing these selected frequencies in a memory forfuture use, and generating the detection field on one the selectedfrequencies having a low noise characteristic. The method alsopreferably includes, on detection of a possible body, changing thegeneration of the detection field to another of the selected frequenciesseparated significantly from the previous frequency, detecting anychange in the phase at the receive antenna, and generating an alarmsignal if such change is detected.

According to another aspect of the invention a sensor for detecting thepresence of an animal body comprises a waveform generator connected to atransmit antenna to create a low frequency electromagnetic detectionfield, a receive antenna spaced from the transmit antenna to measure thedetection field, and analyser means to detect changes in the phasecaused by the presence of the body in the detection field.

In installations of the sensor which serve to protect an area, or anopening to an area, against the intrusion of a body, human or animal, itmay be desirable to distinguish between bodies approaching theprotection field from inside the area and those approaching outside thearea, so that, for example, false alarms are not triggered by themovement of people or animals within the protected area. If the antennaeare installed with a horizontal distance between them, with the transmitantenna closer to the protected area or opening, then the sensor may bearranged to determine from which side the body approaches the detectionfield. It has been found that, from the receive side (i.e. closer to theoutside), the sensor detects an increase in phase change accompanied byan increase in signal amplitude. From the transmit side (i.e. closer tothe inside), the sensor detects zero or very small increases in phasechange, accompanied by a reduction in signal amplitude.

Thus, the invention preferably provides a sensor according to theinvention for detecting the approach of a body towards a protected areaor protected opening to an enclosure, comprising a transmit antennaclose to the protected area or opening and a receive antenna spacedhorizontally from the transmit antenna away from the protected area oropening, and wherein the analyser means is arranged to monitor the phaseand amplitude of the signal received at the receive antenna, and togenerate an alarm signal only in response to a simultaneous increase inamplitude with change in phase.

In an alternative arrangement, permitting more sophisticateddiscrimination, the sensor may include at least one additional receiveantenna, and the analyser is arranged to process signals received by thereceive antennae to detect the direction in which the body moves throughthe detection field and/or the position of the body within the detectionfield. By using a plurality of additional receive antennae located atdifferent positions, it might be possible, for example, to trackmovement of the body more accurately as it approaches to the protectedarea or opening.

The analyser may be connected to receive a reference signal from thewaveform generator and a received signal from the receive antenna, andthe analyser is arranged to equalise the reference signal with thereceived signal to set a base condition of the phase of the signals whenthere is no intrusion of the detection field. In this manner the basecondition can be used as a datum against which variations in the phasecan be detected.

The sensor preferably includes a controller arranged to control thewaveform generator to perform a frequency scan of the frequency spectrumto be used, the analyser is arranged to determine the background noisefor each scanned frequency and to transmit a signal to the controllercommensurate with the background noise associated with each scannedfrequency, and the controller is arranged to identify those scannedfrequencies having the least background noise and to store thisinformation in a memory for future use. The controller is preferablyarranged to cause the waveform generator to transmit at a frequencyhaving low background noise. The analyser is preferably arranged totransmit a detection signal to the controller as soon as a potentialintrusion is detected, the controller is arranged on receipt of adetection signal to cause the waveform generator to transmit at adifferent frequency noted in the memory as having low background noise,and the controller is then arranged to generate an alarm signal onreceipt of a further detection signal from the analyser.

The transmit and receive antennae are preferably positioned to define adetection zone.

The invention can be used in situations in which the reliable detectionof animals is required and, as it does not rely on movement, offersadvantages over current designs. Variants that can be used in thefollowing applications and others are envisaged;

-   -   a) Intruder detection    -   b) Perimeter security    -   c) Access control    -   d) Energy management    -   e) Machine safety    -   f) Marine security    -   g) Automotive security    -   h) Rescue    -   i) Safety

Further features of this invention will be apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example only, with referenceto the accompanying drawings in which:—

FIG. 1 is a block diagram of a sensor illustrating its function, withcontinuous lines showing data transmission and chain-dotted linesshowing transmission of control signals;

FIG. 2 is a block diagram of the analyser; and

FIG. 3 is a block diagram of prototype equipment used to conductexperiments, details of which are set out hereinafter in the Examples.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

With reference to FIG. 1, a sensor comprises a flexible waveformgenerator 10 arranged to produce an analogue LF signal and to transmitthis LF signal 11 to a transmit antenna 12 through a transmit amplifier13, the waveform generator 10 being controlled by a controller 14 whichreceives control signals 15 from an analyser 16. An LF field 17 isgenerated between the transmit antenna 12 and a receive antenna 18 whichtransmits the received signal 19 to the analyser 16 via a receiveamplifier 20.

The basic principle of operation of the sensor is the modification ofthe LF field 17 by the intrusion of a body. A human or animal bodyexhibits values of both conductance and capacitance when intruding intothis LF field, through the parameters of conductivity and permittivity.Whilst the exact scientific analysis is currently uncertain, such anintrusive body appears to act as a dielectric. We have found that, atthe lower end of the preferred frequency range, the intrusive body actsprincipally as a conductor of the LF signals, with some resistive loss,but also displays a capacitive component. Below 100 kHz the capacitiveelement appears to be typically less than 10% of the impedance of thebody, but is higher above 100 kHz.

Although the LF field 17 extends between the transmit antenna 12 and thereceive antenna 18, it also extends around the transmit antenna 12. Insecurity applications, for example, the antennae 12, 18 can bepositioned vertically on the opposite sides of door frames, orhorizontally on the upper and lower edges of window frames. In anothersecurity application, one of the antennae, preferably the transmitantenna 12, can be positioned generally horizontally along a perimeterthat requires protection, with the receive antenna 18 (or antennae)positioned generally vertically within the protected perimeter. Inanother application the intrusion can be detected by two or more receiveantennae which give information about the direction of intrusion and canalso determine the position of the intrusive object within the LF field.

The LF field is established with a frequency preferably up to 200 kHz atlow power and, when this field is disturbed by intrusion of a body, ameasurable amplitude and phase shift is detected by the analyser 16.This shift in the amplitude and phase occurs as an intruder appears toact as a dielectric at these frequencies as indicated above. A set upsignal 21 causes the controller 14 to apply a control signal 22 to setthe frequency range of the waveform generator 10 to comply withfrequency regulatory issues in the vicinity of the sensor, and can alsobe used to omit any frequencies that may be unsuitable for the ambientconditions. The controller 14 also uses the control signal 22 to set theappropriate channel parameters of the waveform generator 10, includingfrequency, amplitude and modulation. The controller 14 transmits afurther control signal 23 to set the gain of the amplifier 13 so thatthe LF signal 11 is amplified to provide a transmission signal along ascreened transmission cable 24 to ensure balanced radiation by thetransmit antenna 12. The LF signal 11 is referred by data line 25 to theanalyser 16 and this signal is compared by the analyser 16 with thereceived signal 26. The analyser 16 then causes the controller 14 tovary the gain of the transmit amplifier 13 to equalise the signal levelsof the reference in data line 25 and the received signal 26. Understable conditions there should be no phase shift between the referencesignal 25 and the received signal 26 other than the constant phasedifference due to the path length between the antennae 12 and 18. Thereceive amplifier 20 is set to balance the gain of the received signal26 with the reference signal 25 so that the analyser 16 can detectshifts in amplitude and/or phase.

The controller 14 receives power via cable 27 and issues alarm signalsalong data line 28 which may communicate through a communicationsinterface (not shown) to operate alarms, such as lights, bells orklaxons, or to alert security personnel or police, or to operate anaccess control system, or to operate an energy management system.

The antennae 12, 18 may be either dipole or monopole and are preferablyprovided with a respective tamper loop 29 operative to detect anytampering with the antennae.

During the set-up routine of the sensor, and without the presence of anyintruder in the LF field 17, the controller 14 performs a frequency scanof the nominal 30 kHz to 300 kHz (preferably up to 200 kHz) spectrum todetermine the background noise environment and to select those channelsthat exhibit least noise characteristics. These selected channels arestored in a memory (not shown) within the controller 14 in priorityorder as the preferred channels. In operation the sensor continuouslymonitors all of the preferred channels as a background task and,provided the LF environment remains stable, transmits on only one of thepreferred channels. When the LF field 17 is disturbed by the intrusionof a body, there will be a phase and/or amplitude shift in the receivedsignal 26 compared with the transmitted signal 11. To ensure that theinitial detection of a phase and/or amplitude shift represents thedetection of an intruder, rather than noise, the controller 14 isarranged to react by selecting another preferred channel from the memory(preferably a channel as widely separated from the initial channel aspossible) and again measure any phase and/or amplitude shift. Shouldthis second detection also prove positive, the controller 14 is arrangedto report an alarm via the alarm data line 28.

FIG. 2 illustrates the arrangement of the analyser 16 to achievereliable detection of intrusion in the LF field 17. FIG. 2 utilises thesame reference numerals as used in FIG. 1 to denote common features.

The received signal 19 is fed through the receive amplifier 20 to reducethe impedance mismatch and to provide a higher level output. A pair ofhigh speed analogue to digital converters 30 and 31 are powered from thecontroller (not shown) through line 32. The reference signal 25 and thereceived signal 26 are converted at high speed to respective digitalsignals 33 and 34 by the respective analogue to digital converters 30and 31. These digital signals 33 and 34 are fed to a dual input phasecomparator 35 which generates a signal 36 commensurate to any phaseshift. A logic filter 37 sets an appropriate threshold to the signal 36and only generates an output signal 38 if this threshold is exceeded.The threshold of the logic filter 37 is set by calling up the phaseshift measured at set-up which is due to the path length between theantennae 12, 18. When this threshold is exceeded, the signal 36 informsthe controller 14 which stores the receive signal in its memory.

The controller is arranged at this juncture to initiate a check forbroadband noise by sampling the receive signal in a multi-element bandfilter 39 connected to the digital output 33 representing the receivedsignal 19. A signal output 40 from the band filter 39 leads to thecontroller but is implemented in software to allow the controllerrapidly to determine the presence of significant high noise levels inadjacent channels. Provided that there is no broadband noise present,the controller next checks for narrow band noise. The reference signalrepresented by the digital signal 34 is now re-sampled along line 41 bya gating circuit 42 operated by the controller by signals along line 43.The gating circuit 42 periodically disables the transmit signal to allowdetection of any unwanted transmission at the currently selected receivefrequency. The digital signal 33 representing the received signal 19 isnow sampled by a noise detector 44—under conditions of no transmitsignal, the received signal 19 should only contain extraneous background noise.

The output signal 45 from the noise detector 44 is fed to a dual inputsubtractor 46 where its amplitude is subtracted from the amplitude ofthe initial detection signal that was stored by the controller and ispassed to the subtractor 46 along line 47. The output from thesubtractor 46 is passed along a line 48 to for thresholding. When theinitial detection signal is significantly higher than the backgroundnoise level, the controller is informed by a signal along line 38.

Having detected both phase and amplitude shifts, the controller nowswitches to a new preferred channel of which the frequency is optimallyas far away as possible from the original channel. The entire process isthen repeated in order to validate, or invalidate, the presence of anintruding body, thereby improving the robustness of detection by thesensor. A second positive detection of phase and amplitude shift in thenew channel is taken as confirmation of an intruder in the LF field andthe controller will, as already described with reference to FIG. 1, sendan alarm signal down the alarm data line 28.

Should broadband noise be detected, for instance generated by lightningor by deliberate jamming, then the analyser 16 does not declaredetection of an intruder but the controller 14 enters a routine toattempt to find a “clean” channel. The presence of lightning is likelyto be transient, but should jamming be employed in an attempt to foolthe sensor, the controller 14 will pass an alarm alert signal down thealarm data line 28. However, should narrow band noise be detected, thecontroller 14 will merely switch to a new channel and continue tooperate normally.

The key to sensor operation and performance is the generation of the LFfield and detecting the effects of its disturbance by the intrusion of abody.

Experiments have been carried out which practically demonstrate proof ofthe LF field generation and the detection of intrusion into the field bya person.

Computer modelling has also been carried out using specialist programsto plot the field patterns of various antenna arrangements and tosimulate the effects of field disturbance.

Both the experimental and the modelling approaches have confirmed therobustness of the technology and confirm its suitability for use as apractical sensor system.

EXAMPLES

Prototype equipment has been used for various performance proving tests.The prototype equipment used for the experiments was configured as shownin FIG. 3. A low power continuous wave RF signal at a nominal frequencyof 100 kHz is generated in a Function Generator 7. The device used wasthe Velleman PCG-10 which is PC controlled (not shown). The signal ispassed along signal line 10, firstly to an Amplifier 8 and secondly toprovide input to a monitor Oscilloscope 6 and Timer/Counter 5. TheAmplifier 8 output is passed by signal line 11 to a Matching Circuit 9.The Matching Circuit is a series of inductors which can be switched toprovide an optimised match between the Amplifier and Transmit Antenna 2dependant on the length of the Transmit Antenna.

The receive signal is passed from the Receive Antenna 1 to a MatchingCircuit 3 which performs a similar function to the one used in thetransmit channel. The signal is then passed via signal line 12 to aPre-Amplifier 4 and then via signal line 13 to the monitor Oscilloscope6 and Timer/Counter 5.

On initial set up, the transmit signal level is selected at the FunctionGenerator 6. To optimise the match and therefore the transfer efficiencyof the signal, the output of the Matching Circuit 9 is monitored on theOscilloscope 6 whilst the Matching Circuit 9 is switched between aseries of inductive loads. When a peak level is obtained, the match isdeemed to be satisfactory. The same process is used to optimise thematch in the receive channel, except that here the monitor point is atthe output of the Pre-Amplifier 4. The Oscilloscope 6 and Timer/Counter5 are then used to display the condition of the RF field by monitoringthe sample transmit signal and the receive signal, with the Oscilloscope6 being used to demonstrate the amplitude and phase relationship betweenthe transmit and received signals. Dependant upon the size of phaseangle change, the effect can be seen by visual comparison between thetwo sine waves. For better resolution the Timer/Counter 5 can be set todisplay the time differences between the leading edge of the transmitsignal and receive signal, allowing phase angle changes to be morereadily determined.

The set-up is completed in conditions of no animal presence in thefield, and when the field is disturbed by an animal or animals thechanges in phase angle and amplitude can be determined.

The experiments listed below are examples to illustrate the capabilityof the detection sensor in a wide range of potential applications forwhich the ability to detect animal presence reliably is a requirement.These results are typical of the prototype; improvements are anticipatedfrom continuing developments in-hand or planned.

a) Intruder Detection—Window Opening Antenna length (Rx & Tx) 1.5 mAntenna location (Rx) Beneath cill Antenna location (Tx) On floorFrequency 100 kHz Minimum phase change  0.2 degrees Maximum phase change120 degrees Detection range 2.5 m

Note: This configuration enables direction of approach to be determinedby comparing phase change with amplitude change. From outside theproperty the phase change caused by a disturbance in the field spans theminimum to maximum and is accompanied by an increase in amplitude, frominside the property the phase change is much less and accompanied by areduction in amplitude.

b) Intruder Detection—Door Opening Antenna length (Rx & Tx) 1.5 mAntenna location (Rx) On floor Antenna location (Tx) On floor Frequency100 kHz Minimum phase change 0.5 degrees Maximum phase change  60degrees Detection range 1.5 m

Note: This configuration enables direction of approach to be determinedby comparing phase change with amplitude change. From outside theproperty the phase change caused by a disturbance in the field spans theminimum to maximum and is accompanied by an increase in amplitude, frominside the property the phase change is much less and accompanied by areduction in amplitude.

c) Perimeter Protection Antenna length (Rx) 60 m Antenna length (Tx)  1m Antenna location (Rx)  1 m above ground Antenna location (Tx) Closecoupled Frequency 100 kHz Minimum phase change 0.5 degrees Maximum phasechange  45 degrees Detection range  2 m

Note: In this configuration the Tx antenna is closely-coupled to the Rxby winding it around the feed.

d) Energy Management (Detecting the Presence of a Person within a Roomand Switching Off Light/Heat when None Detected) Antenna length (Rx) 10m (coiled) Antenna length (Tx) 20 m Antenna location (Rx) On ceilingAntenna location (Tx) On floor Frequency 100 kHz Minimum phase change0.5 degrees Maximum phase change  90 degrees Detection range See note

Note: In this configuration the Tx antenna is looped under a floorcovering with the Rx antenna as a coil in the ceiling, of 100-150 mmdiameter. Detection of animals within a room is possible. The experimentwas conducted in a 5 m×5 m room, with 2.5 m ceiling height.

1. A method of detecting an animal body, comprising generating a lowfrequency radio (LF) detection field and detecting a phase change in thefield caused by the presence of the body in the detection field.
 2. Amethod according to claim 1, including using a transmit antenna togenerate the LF field and using a receive antenna to detect any changein the detection field.
 3. A method according to claim 2, includingusing at least one additional receive antenna, and using the output fromthe receive antennae to detect the direction in which the object movesthrough the detection field and/or the position of the object within thedetection field.
 4. A method according to claim 2 for detecting theapproach of a body towards a protected area or protected opening to anenclosure, including using a transmit antenna close to the protectedarea or opening and a receive antenna spaced horizontally from thetransmit antenna away from the protected area or opening, monitoring thephase and amplitude of the signal received at the receive antenna, andgenerating an alarm signal only in response to a change in phaseaccompanied by an increase in amplitude.
 5. A method according to anypreceding claim, including detecting the change in the detection fieldby measuring the phase of the signal received at a receive antenna inthe absence of any animal in the detection field, and by monitoring thereceived signal to determine when the phase of the signal has changed bymore than a predetermined amount.
 6. A method according to any of claims1 to 4, including taking a reference signal from a transmission signalto the transmit antenna, and equalising this reference signal with areceived signal from the receive antenna to ensure that there will be nophase shift between the transmission signal and the received signal inthe absence of a body.
 7. A method according to any preceding claim,which comprises generating the LF detection field using a modulated LFsignal.
 8. A method according to any preceding claim, including samplingthe transmitted and received LF signals in the absence of a body, usingthese samples to determine a base condition for the phase value, andcomparing the received signal with this base condition.
 9. A methodaccording to claim 8, including determining the base conditions at twoor more LF frequencies, generating the detection field at one frequencyuntil the possible presence of an animal body is detected with referenceto the base condition at that frequency, and then changing the LFfrequency to confirm such intrusion with reference to the base conditionat the second frequency.
 10. A method according to any preceding claim,including performing a frequency scan of the frequency spectrum to beused to determine the background noise environment, selecting thefrequencies which exhibit least noise characteristics, storing theseselected frequencies in a memory for future use, and generating thedetection field on one the selected frequencies having a low noisecharacteristic.
 11. A method according to claim 10, including, ondetection of the possible presence of an animal body, changing thegeneration of the detection field to another of the selected frequenciesseparated significantly from the previous frequency, detecting anychange in the phase at the receive antenna, and generating an alarmsignal if such change is detected.
 12. A sensor for detecting thepresence of an animal body, comprising a waveform generator connected toa transmit antenna to create a low frequency electromagnetic detectionfield, a receive antenna spaced from the transmit antenna to measure thedetection field, and analyser means to detect a change in the phase ofthe received signal caused by the presence of the body in the detectionfield.
 13. A sensor according to claim 12 for detecting the approach ofa body towards a protected area or protected opening to an enclosure,comprising a transmit antenna close to the protected area or opening anda receive antenna spaced horizontally from the transmit antenna awayfrom the protected area or opening, and wherein the analyser means isarranged to monitor the phase and amplitude of the signal received atthe receive antenna, and to generate an alarm signal only in response toa change in phase accompanied by an increase in amplitude.
 14. A sensoraccording to claim 12, including at least one additional receiveantenna, and in which the analyser means is arranged to process signalsreceived by the receive antennae to detect the direction the body movesthrough the detection field and/or the position of the body within thedetection field.
 15. A sensor according to claim 12, 13 or 14, in whichthe analyser means is connected to receive a reference signal from thewaveform generator and a received signal from the receive antenna, andthe analyser is arranged to equalise the reference signal with thereceived signal to set a base condition of the phase of the signals whenthere is no animal body present in the detection field.
 16. A sensoraccording to any of claims 12 to 15, including a controller arranged tocontrol the waveform generator to perform a frequency scan of thefrequency spectrum to be used, the analyser being arranged to determinethe background noise for each scanned frequency and to transmit a signalto the controller commensurate with the background noise associated witheach scanned frequency, the controller being arranged to identify thosescanned frequencies having the least background noise and to store thisinformation in a memory for future use.
 17. A sensor according to claim16, in which the controller is arranged to cause the waveform generatorto transmit at a frequency having low background noise.
 18. A sensoraccording to claim 16 or 17, in which the analyser is arranged totransmit a detection signal to the controller as soon as a potentialintrusion is detected, the controller is arranged on receipt of adetection signal to cause the waveform generator to transmit at adifferent frequency noted in the memory as having low background noise,and the controller is then arranged to generate an alarm signal onreceipt of a further detection signal from the analyser.